The present invention relates to methods and apparatus for printing a graphic product on sheet material in accordance with a printing program and stored data representative of the graphic product, and more particularly to methods and apparatus for printing a wide format multicolor graphic product on a printing sheet, such as a vinyl sheet for use as signage.
Known in the art are thermal printing apparatus for generating signs, designs, characters and other graphic products on a printing sheet in accordance with a printing program and data representative of the graphic product. Typically, a thermal printer interposes a donor sheet that includes donor material and a backing between a thermal printhead and the printing sheet. The thermal printhead includes an array of thermal printing elements. The thermal printhead prints by pressing the donor sheet against the printing sheet and selectively energizing the thermal printing elements of the array, thereby selectively transferring pixels of donor medium from the donor sheet to the printing sheet. Movement of the printing sheet relative to the thermal printhead (or vice versa) while pressing the donor sheet against the printing sheet with the thermal printhead draws fresh donor sheet past the thermal printhead. The printing sheet typically includes a vinyl layer secured to a backing layer by a pressure sensitive adhesive so that after printing the vinyl bearing the graphic product can be cut and stripped from the backing material and affixed to an appropriate sign board or other material for display.
The proper printing of many graphic products, such as commercial artwork or signage, can require high quality print work. Often, it is desired that the final multicolor graphic product be physically large, such as several feet wide by tens of feet long. Typically, existing thermal printers are limited in the width of printing sheet that they can print upon. For example, one popular thermal printer prints on sheets that are one foot wide. Accordingly, the final graphic product is often assembled from separately printed strips of printing sheet that must be secured to the signboard in proper registration with one another. Often, the registration is less than perfect and the quality of the final graphic product suffers, especially when backlit.
Wide format thermal printers are known in the art. For example, one wide format thermal printer currently available can accommodate a printing sheet up to three feet wide and uses four full width (i.e., three feet wide) printheads, each interposing a different color donor sheet between the printhead and the printing sheet. Accordingly, far fewer seams, if any at all, require alignment when creating the sign or other product. Also, the use of four printheads allows faster printing of the multicolor graphic product.
Unfortunately, this type of machine can be expensive to manufacture and to operate. For example, each printhead, at a typical resolution of 300 dpi, includes literally thousands of thermal printing elements, all of which are typically required to have resistances that are within a narrow tolerance range. Such a thermal printhead is difficult and expensive to manufacture, and moreover, burnout of simply a few thermal printing elements can require replacement of the entire printhead. Furthermore, donor sheet is also expensive, and the full-width printing heads can be wasteful of donor sheet when printing certain types of, or certain sections of, graphic products. For example, consider that a single color stripe one inch wide and perhaps a foot long is to be printed in center of the printing sheet. Though the printed object occupies {fraction (1/12)} of a square foot, an area of donor sheet that is three feet wide by one foot long, or three square feet, is transferred past the print head when printing the above object, and hence consumed. The printing of a wide format graphic product that includes a narrow border about the periphery of the printing sheet is another example that typically can be wasteful of donor sheet when printing with the above wide format thermal printer.
Other wide format printers are known in the art, such as wide format ink-jet printers, which can also print in a single pass. However, ink-jet printed multicolor graphic products are typically not stable when exposed to the elements (e.g., wind, sun, rain) or require special post-printing treatment to enhance their stability, adding to the cost and complexity of printing with such apparatus.
Accordingly, it is an object of the present invention to address one or more of the foregoing and other deficiencies and disadvantages of the prior art.
Other objects will in part appear hereinafter and in part be apparent to one of ordinary skill in light of the following disclosure, including the claims.
In one aspect, the invention provides an apparatus for supporting a sheet material on a worksurface with a selected alignment and for performing work operations on the sheet material responsive to a controller. The apparatus includes a workbed providing the worksurface for supporting the sheet material, where the worksurface contains a workhead axis and a sheet material translation axis perpendicular to the workhead axis; a workhead for performing the work operation upon the sheet material, the workhead being translatable parallel to the work axis for printing on the sheet material; means for securing the sheet material to the worksurface when working on the sheet material and for releasing the sheet material from the worksurface when translating the sheet material; sensing means for sensing an edge of the sheet material; and sheet material translation means for translating the sheet material in the direction of the sheet material translation axis. The sheet material translation means includes means for differentially driving spaced portions of the sheet material, responsive to the sensing means, for providing a selected alignment of the sheet material relative to the worksurface.
In another aspect, the invention provides an apparatus for supporting a sheet material on a worksurface with a selected alignment for performing work operations on the sheet material. The apparatus includes a workbed for providing the worksurface for supporting the sheet material, where the worksurface containing a work axis and sheet material translation axis perpendicular to the work axis; sheet material translation means for translating the sheet material in the direction of the sheet material translation axis; a workhead for performing the work operations upon the sheet material, the workhead being translatable parallel to the work axis; means for securing the sheet material to the worksurface when printing on the sheet material and releasing the sheet material from the worksurface when translating the sheet material; and an edge sensor for sensing an edge of the sheet material. The sensor is mounted with the workhead for translation therewith in the direction of the work axis.
The apparatus also includes a controller in communication with the workhead, the sheet material translation means and the sensing means for controlling the work operation on the sheet material responsive to data stored in a memory. The controller includes programming, stored in a memory associated therewith, for determining the alignment of the sheet material, the programming including instructions for the following: translating the workhead in the direction of the work axis and past the edge of the sheet; receiving a first communication from the edge sensor responsive to the location of the edge of the sheet material in the direction of the work axis; energizing the sheet material translation means for translating the sheet material a known distance in the direction of the sheet material translation axis; translating the workhead in the direction of the work axis and past the edge of the sheet; receiving a second communication from the edge sensor responsive to the location of the edge of the sheet material in the direction of the work axis; and determining the skew of the sheet material responsive to the first and second communications and the known translation distance.
In yet another aspect, the invention provides an apparatus for supporting a sheet material on a worksurface with a selected alignment for performing work operations on the sheet material. The apparatus includes a workbed for providing the worksurface for supporting the sheet material, where the worksurface containing a work axis and sheet material translation axis perpendicular to the work axis; sheet material translation means for translating the sheet material in the direction of the sheet material translation axis; a workhead for performing the work operations upon the sheet material, the workhead being translatable parallel to the work axis; means for securing the sheet material to the worksurface when printing on the sheet material and releasing the sheet material from the worksurface when translating the sheet material; and an edge sensor for sensing an edge of the sheet material, where the sensor is mounted with the workhead for translation therewith in the direction of the work axis.
The apparatus further includes a controller in communication with the workhead, the sheet material translation means and the edge sensor for controlling the work operation on the sheet material responsive to data stored in a memory. The controller further includes programming, stored in a memory associated therewith, for determining the alignment of the sheet material. The programming includes instructions for the following: translating the workhead in the direction of the work axis and past the edge of the sheet; receiving a first communication from the edge sensor responsive to the location of the edge of the sheet material in the direction of the work axis; energizing the sheet material translation means for translating the sheet material a known distance in the direction of the sheet material translation axis; translating the workhead in the direction of the work axis and past the edge of the sheet; receiving a second communication from the edge sensor responsive to the location of the edge of the sheet material in the direction of the work axis; and determining the skew of the sheet material responsive to the first and second communications and the known translation distance.
In yet an additional aspect, the invention includes an edge detection system for providing signals to a controller for detecting the edge of a sheet material in an apparatus that includes a worksurface for supporting the sheet material, drive means for translating the sheet material along a sheet material translation axis and a workhead translatable along a work axis perpendicular to the sheet material translation axis for performing work operations on the sheet material. The edge detection system includes a first sensor mounted for translation in the direction of the work axis along with the workhead and facing the worksurface for detecting light traveling in a direction upward from the worksurface toward the sensor; and a second sensor for providing signals responsive to the position of the first sensor in the direction of the work axis.
In a further aspect, the invention includes a method of aligning a sheet material disposed upon a worksurface for enhancing printing or other operations on the sheet material. The method includes the following steps: placing the sheet material over the worksurface; determining the alignment of the sheet material in a coordinate system having first and second axes for specifying locations relative to the worksurface and the sheet material overlaying the worksurface; and differentially driving spaced portions of the sheet material for moving the sheet material for providing a selected alignment of the sheet material.
In general, the invention is deemed useful in many environments where a workbed includes a worksurface for supporting a sheet material on which work operations are to be performed. For example, xe2x80x9cwork operationsxe2x80x9d can include, but is not limited to, plotting, cutting or printing, such that the workhead mounts, as is appropriate, a pen; cutter, such as a knife; roller or laser cutter; or a printhead, such as a thermal printhead.